The invention relates to cushioning devices mounted on the ends of rail cars to cushion buff and draft impacts exerted on the couplers by an adjacent rail car.
Cushioning units are conventionally mounted in pockets at the ends of the center sill of a rail car. The rail cars are joined together to form a train by pairs of knuckle couplers connected to the cushioning units. The train may be 50 or more cars long and drawn by one or more locomotives. The pairs of knuckle couplers provide approximately 2 inches of free movement or slack between adjacent cars. This slack permits the rail cars limited movement toward and away from each other in response to train action events including locomotive traction and braking, differences in braking forces of adjacent cars and gravity-induced movement of the cars as the train moves onto and away from inclines.
Train action events subject the couplers of joined cars to buff and draft impacts which, if undamped, are transmitted directly to the rail cars and subject the cars and lading to undesirable high accelerations. The accelerations can injure lading on the rail cars.
In some train action events, including locomotive start up and acceleration, traction braking and movement of the train onto and from inclines, slack is taken up between adjacent cars beginning at one end of the train and ending at the other end of the train. As a result of slack being progressively taken up the speed differences between the cars as the slack at each coupler pair is taken up increases, with a resultant increase in the buff and draft impacts on the couplers. For instance, during locomotive acceleration of a 50 car train from rest there is a total of 100 inches of slack between the 50 pairs of couplers in the train. This slack is taken up progressively, coupler pair by coupler pair. When the 2 inch slack in the coupler pair joining the last car to the train is taken up the next to the last car may be moving to a speed of 4 miles an hour. The slack in the last coupler pair is taken up very rapidly and the last two cars are subjected to a very large impact capable of injuring lading.
Trains are made up in rail yards, conventionally by rolling individual cars into stationary cars so that the knuckle couplers are engaged. Relative high speed rolling of cars against stationary cars subjects both cars to high buff impacts which are capable of injuring lading on the cars.
Conventional end of car rail car cushioning units do not efficiently cushion impacts from train action events, both in buff and draft, and do not efficiently cushion high buff impacts experienced during train make-up.
The invention is an improved end of car rail car cushioning device for cushioning train action buff and draft impacts and for cushioning buff impacts during train makeup. The unit is self-centering after both buff and draft impacts and includes a gas charged hydraulic cylinder and an elastomer spring mounted between the rail car and a coupler at the end of the car. The piston in the cylinder is normally located in a neutral position between the front and rear heads of the cylinder and is moveable in either direction in response to buff and draft impact movement of the coupler to displace hydraulic fluid from the cylinder and hydraulically cushion buff and draft impacts.
During buff impacts, the elastomer spring is free of the coupler as the cylinder moves along a long buff stroke and absorbs energy. During the final 2 inches of buff stroke, the elastomer spring is joined to the coupler in parallel with the hydraulic cylinder and both the cylinder and the spring absorb energy. The elastomer spring prevents the unit from bottoming and protects the lading from high accelerations.
During draft impacts the cylinder and spring are joined to the coupler in parallel and both absorb impact energy along a short 2 inch draft stroke. The spring prevents bottoming and protects lading from high accelerations.
The elastomer spring has a collapse stroke of approximately 2 inches, and nonlinear characteristics with a very high spring rate near the end of its stroke, which assures that nearly all impacts, both in buff and draft, are fully absorbed before the cushioning device bottoms and impact force is transmitted directly to the rail car. The long buff stroke facilitates hydraulic absorption of high energy buff impacts during train make up.
Spring backed valves are mounted in flow orifices in the hydraulic cylinder to either side of the neutral position. These valves crack open only after a buff or draft force exerted on the coupler exceeds a minimum force. The high coupler forces required to crack open the spring backed valves assures that the cushioning unit holds the coupler in place when subjected to low energy buff and draft impacts which do not injure lading, yet collapses and absorbs energy when high force impacts are experienced, in both buff and draft. The ability to keep the cushioning unit stiff during low level impacts reduces movement between adjacent rail cars and helps reduce impact injury to lading.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are five sheets and one embodiment.